Influence of Impurities on the Luminescence Quantum Efficiency of ( La , Ce , Tb ) PO 4

The influence of impurities on the luminescence quantum efficiency of and has been studied. The transition metal ions Fe and Mn are not built into the lattice under a reducing firing atmosphere. Tetravalent Ce 4+ is probably present in a second phase. Codoping with cations with different valencies has no influence on the Ce 4+ amount nor on the Ce 3+ quantum efficiency. The energy transfer rate from Ce 3+ to a number of rare‐earth ions (Pr 3+ , Nd 3+ , Dy 3+ , Ho 3+ , Er 3+ ) is low. Therefore, low concentrations of these ions do not compete efficiently with the Tb 3+ ion for the excitation energy on the Ce 3+ ion. However, the Ce 3+ quantum efficiency is reduced by Eu 3+ due to an electron transfer process. Energy transfer between Tb 3+ ions is restricted to Tb 3+ clusters, so that the probability that the excitation energy reaches impurities is low. Therefore low concentrations of rare‐earth ions have only a small effect on the Tb 3+ quantum efficiency.